This invention relates to an accumulator with an integral heat exchanger for use in an air conditioning or refrigeration system. In particular, the heat exchanger is positioned inside the accumulator such that liquid refrigerant from the high pressure, high temperature side of the system and gaseous refrigerant from the low pressure, low temperature side of system simultaneously flow through the heat exchanger in a heat exchange relationship. The accumulator of the present invention may be used with a variety of refrigerants including R134a and carbon dioxide, despite the higher operating pressures inherent in a system using carbon dioxide as the refrigerant.
A basic refrigeration or air conditioning system has a compressor, a condenser, an expansion device, and an evaporator. These components are generally serially connected via conduit or piping and are well known in the art. During operation of the system, the compressor acts on relatively cool gaseous refrigerant to raise the temperature and pressure of the refrigerant. From the compressor, the high temperature, high pressure gaseous refrigerant flows into the condenser where it is cooled and exits the condenser as a high pressure liquid refrigerant. The high pressure liquid refrigerant then flows to an expansion device, which controls the amount of refrigerant entering into the evaporator. The expansion device lowers the pressure of the liquid refrigerant before allowing the refrigerant to flow into the evaporator. In the evaporator, the low pressure, low temperature refrigerant absorbs heat from the surrounding area and exits the evaporator as a saturated vapor having essentially the same pressure as when it entered the evaporator. The suction of the compressor then draws the gaseous refrigerant back to the compressor where the cycle begins again.
In a typical air conditioning or refrigeration system, it is necessary to prevent liquid from passing from the evaporator into the compressor in order to avoid damage to the compressor. When liquid refrigerant enters a compressor, it is known as slugging. Slugging reduces the overall efficiency of the compressor and can also damage the compressor. It is well known in the art to mount a suction line or low pressure side accumulator between the evaporator and compressor. Such suction line accumulators act to separate the liquid and gaseous phases of the refrigerant flowing from the evaporator. The liquid portion of the refrigerant will settle to the bottom of the accumulator while the gaseous phase will rise to the top of the accumulator and will be suctioned out of the accumulator by the compressor.
It is also known in the art to have an accumulator with a heat exchanger arranged on both the high pressure and low pressure sides of an air conditioning or refrigeration system. FIG. 1 is a schematic of a system having an accumulator arranged on both the high pressure and low pressure sides of the system. In general, high pressure, high temperature refrigerant exits a compressor 1 and flows into a condenser 3. The high temperature liquid refrigerant exits the condenser and flows into a heat exchanger located in an accumulator 5. The refrigerant is discharged from the accumulator and flows into an expansion device 7 and subsequently into an evaporator 9.
At the same time, low temperature, low pressure refrigerant flowing from the evaporator 7 enters the accumulator and the liquid phase settles to the bottom of the accumulator, and the gaseous phase rises. The low temperature gaseous refrigerant then flows through the heat exchanger where it comes in contact with the high pressure, high temperature liquid refrigerant from the condenser in a heat exchange relationship. The high pressure liquid from the condenser 3 is then cooled by the low pressure, low temperature gaseous refrigerant running simultaneously through the heat exchanger. As a result, the liquid refrigerant flowing from the condenser 3 to the evaporator is cooled and can thereby absorb more heat as it flows through the evaporator 7. The gaseous refrigerant exiting the low pressure side of heat exchanger is higher in temperature having absorbed heat from the high pressure, high temperature liquid refrigerant. As a result, any liquid refrigerant that may remain in the low pressure, low temperature refrigerant will be converted into a gas in the heat exchanger thereby reducing the risk of having liquid flow into the compressor.
U.S. Pat. Nos. 5,622,055, 5,245,833, 4,488,413, and 4,217,765 disclose accumulators with internal heat exchangers. In these patents, high pressure, high temperature refrigerant from the condenser is cooled as it flows through a tube that is sitting in a pool of low temperature liquid refrigerant that has been discharged from the evaporator and collected in the accumulator.
GB Patent No. 2316738B also discloses a low pressure side accumulator with an internal heat exchanger. The accumulator is divided into an upper and lower chamber. The heat transfer unit, two serially connected tubes, is housed in the lower chamber. High temperature, high pressure refrigerant flowing from the condenser enters one end of the tubes and exits the other end and then flows to an expansion device evaporator. At the same time, low pressure, low temperature refrigerant from the evaporator is discharged into the upper chamber. The refrigerant in the upper chamber is drawn into the lower chamber where it flows through the lower chamber in a heat exchange relationship with high pressure, high temperature refrigerant flowing through the tubes before being discharged from the accumulator and drawn back to the compressor.
U.S. Pat. Nos. 5,457,966 and 5,289,699 disclose a high pressure side accumulator with internal heat exchanger. In one embodiment, the heat exchanger comprises an outer shell with right and left end plates and an outer tube with a cutaway portion located within the shell. An inner tube is housed within the outer tube and extends through the shell and both end plates. In operation, high pressure, high temperature liquid refrigerant from the condenser enters an inlet line, which flows into the outer tube. The liquid refrigerant flows through the outer tube and into the shell at the cut away portion. The liquid refrigerant is discharged from the shell through an outlet line. At the same time, low pressure, low temperature refrigerant from the evaporator enters the smaller tube and flows through the inner tube in a heat exchange relationship with the high pressure, high temperature refrigerant before flowing back to the compressor.
In a second embodiment, the heat exchanger housed within the shell comprises a small oval shaped tube affixed to one side of a large tube. The larger tube extends through the entire length of the shell. High pressure, high temperature liquid refrigerant from the condenser enters one end of the oval shaped tube and exits the other end and flows into the shell. Liquid refrigerant exits the shell through an outlet line and flows to the evaporator. Simultaneously, low pressure, low temperature refrigerant flows from the evaporator through the large tube in a heat exchange relationship with the high pressure, high temperature refrigerant. The low pressure, low temperature refrigerant exiting the larger tube flows back to the compressor. A third embodiment is similar to the second embodiment except that the smaller tube is spirally wrapped around the outside of the larger tube.
U.S. Pat. No. 3,830,077 discloses a heat exchanger for use in a vehicle, which is connected between the evaporator and compressor. The heat exchanger comprises an outer shell with low pressure, low temperature inlet and outlet lines and at least one heat exchange coil, with an inlet end an outlet end both extending through the shell. In operation, low pressure, low temperature refrigerant enters the inlet line, flows through the shell, exits the outlet line and flows back to the compressor. At the same time a high temperature vehicle fluid flows through the coil in a heat exchange relationship with the low temperature, low pressure refrigerant. The patent does not specifically disclose connecting the heat exchange coil to the high pressure, high temperature side of the air conditioning system.
Finally, published EP Patent Application No. EP 0837291A2 discloses the use of a sub cooling circuit to cool high pressure, high temperature carbon dioxide refrigerant in a vehicle air conditioning system. The sub cooling circuit is located between the condenser and main expansion device and comprises a subpressure reducer and a heat exchanger. In operation, the high pressure, high temperature carbon dioxide refrigerant from the condenser is split into two flows, the first flow flows into the sub cooling circuit where it is cooled by passing through the pressure reducer before flowing through heat exchanger. The second flow of refrigerant passes directly through the heat exchanger where it is cooled by the first flow.
The application discloses two different types of heat exchangers. The first heat exchanger comprises a double circular tube structure which has an inner tube surrounded by an outer tube with fins separating the tubes. Lower temperature carbon dioxide refrigerant flows through the inner tube in a heat exchange relationship with higher temperature refrigerant flowing through the outer tube.
The second heat exchanger comprises a spiral tube structure formed from two tubes soldered together. Each tube is an extruded aluminum strip with an upper row of holes and a lower row of holes. High temperature carbon dioxide refrigerant flows through both rows of holes in one tube while lower temperature refrigerant flows through both rows of holes in the second tube in a heat exchange relationship. EP Patent Application No. 0837291A2 does not disclose having high temperature and low temperature refrigerant flowing through one tube at the same time.
Furthermore, EP Patent Application No. 0837291A2 does not disclose combining the heat exchanger in the sub cooling circuit into an accumulator. Thus, the disclosed air conditioning system is more complicated than necessary having an extra sub cooling circuit, which can be eliminated by the present invention.
While the above accumulators and heat exchangers are suitable for their intended purpose, it is believed that there is a demand in the industry for an improved accumulator with an internal heat exchanger, especially one that can withstand the higher pressure requirements of an air conditioning or refrigeration system employing carbon dioxide as a refrigerant. It is further believed that there is a demand for an improved accumulator with an internal heat exchanger that is compact, easily assembled, lighter weight, and less costly to manufacture, but yet provides a high level of efficiency.
The present invention provides an improved accumulator for use in an air conditioning or refrigeration system, and in particular, provides an accumulator with an improved compact heat exchanger. The improved accumulator may be used in existing air conditioning and refrigeration systems utilizing R134a as the refrigerant as well as in newer systems utilizing carbon dioxide as the refrigerant. The improved accumulator can easily withstand the higher pressures resulting from the use of carbon dioxide refrigerant.
The improved heat exchanger has a high heat transfer efficiency resulting in an increase in the coefficient of performance (COP) for the air conditioning or refrigeration system. As a result, the air conditioning or refrigeration system has greater cooling capacity. This greater cooling capacity allows for more rapid xe2x80x9cpull downxe2x80x9d or cooling when the air conditioning or refrigeration system is first started.
In addition, the accumulator of the present invention provides increased protection against slugging in the compressor by ensuring that any liquid remaining in the refrigerant being drawn back into the compressor is vaporized in the heat exchanger. Finally, the heat exchanger of the present invention is easy to manufacture and is lighter in weight because all of the components may be made from aluminum.
According to one embodiment of the present invention, the accumulator has a housing with a top and a bottom such that the housing, top, and bottom form a chamber. The accumulator has a high pressure outlet port and a low pressure inlet port extending through the top and into the chamber, and a high pressure inlet port and a low pressure outlet port which are external to the housing. A vapor conduit tube and a heat exchanger are disposed in the chamber. The heat exchanger comprises at least one tube having a low temperature channel and a high temperature channel, each channel extending through the interior of the tube. At one end of the tube, the high temperature channel is connected to the high pressure inlet port and the low temperature channel is connected to the low pressure outlet port. At the other end of the tube, the high temperature channel is connected to the high pressure outlet port and the low temperature channel is connected to the vapor conduit tube.
In operation, high pressure, high temperature refrigerant from the condenser enters the accumulator and then the heat exchanger through the high pressure inlet port. The high pressure, high temperature refrigerant flows through the high temperature channel and exits the heat exchanger and the accumulator through the high pressure outlet port. Simultaneously, low pressure, low temperature refrigerant flows through the low temperature inlet port into the chamber and is conveyed through the vapor conduit tube to the heat exchanger. The low pressure, low temperature refrigerant then flows through the low temperature channel in a heat exchange relationship with the high pressure, high temperature refrigerant flowing through high temperature channel thereby cooling the high pressure, high temperature refrigerant.
In a second embodiment of the present invention, the accumulator likewise has a housing with a top and bottom such that the housing, top and bottom form an internal chamber. High pressure, high temperature inlet and outlet ports as well as low temperature inlet and outlet ports extend through the top of the accumulator into the chamber. A vapor conduit tube and a heat exchanger are disposed in the chamber. The heat exchanger comprises a coaxial tube having an outer tube and an inner tube disposed within the outer tube. At one end of the coaxial tube, the high pressure, high temperature inlet port is attached to the inner tube and the low pressure, low temperature outlet port is attached to the outer tube. At the other end of the coaxial tube the high pressure, high temperature outlet port is attached to inner tube and the vapor conduit tube is attached to the outer tube.
In operation, high pressure, high temperature refrigerant from the condenser enters the accumulator and then the heat exchanger through the high pressure inlet port. The high pressure, high temperature refrigerant flows through the inner tube and exits the heat exchanger and the accumulator through the high pressure outlet port. Simultaneously, low pressure, low temperature refrigerant flows through the low temperature inlet port into the chamber and is conveyed through the vapor conduit tube to the heat exchanger. The low pressure, low temperature refrigerant then flows through the outer tube in a heat exchange relationship with the high pressure, high temperature refrigerant flowing through the inner tube thereby cooling the high pressure, high temperature refrigerant.
In a third embodiment of the present invention, the accumulator has a housing, a top, and a bottom such that the housing, top, and bottom form a chamber. The chamber is divided into an upper chamber and a lower chamber by a separator. The accumulator further has low pressure inlet port and a vapor conduit extending through the top, the upper chamber and the separator before terminating in the lower chamber. The internal heat exchanger comprises a plurality of coaxial tubes, each coaxial tube having an outer tube and an inner tube disposed within the outer tube. The inner tubes of the coaxial tubes extend through the top, upper chamber, separator, lower chamber and bottom of the accumulator. The outer tubes extend from the top in the upper chamber through the separator and terminate in the lower chamber. The inner tubes are interconnected to allow refrigerant to circulate through each inner tube.
In operation, the high pressure, high temperature refrigerant flows from the condenser and enters the connected inner tubes. The refrigerant flows through the tubes before being discharged from the accumulator. At the same time, low pressure, low temperature refrigerant from the evaporator enters the low pressure inlet port and flows into the accumulator. The low pressure, low temperature refrigerant then flows through the outer tubes in a heat exchange relationship with the refrigerant flowing through the inner tubes and is deposited in the lower chamber.
The low pressure, low temperature refrigerant is then drawn into the vapor conduit tube and is discharged from the accumulator.
Further features and advantages of the present invention will be apparent upon reviewing the following detailed description and accompanying drawings.